1. Field of the Invention
This invention relates to a lash adjustment system for internal combustion engines and, more particularly, to a lash adjustment system which can adjust valve clearances of intake and exhaust valves by only one lash adjuster.
2. Description of Related Art
In general, valve operations of intake and exhaust valves is achieved by receiving power from a crank shaft.
Valve timing of the intake and exhaust valves has an effect on power of the internal combustion engine. The intake valve opens before an intake stroke of a piston (just before completion of an exhaust stroke) and closes after the piston has passed a bottom dead center of the exhaust stroke.
The reason why the valve operating timing is provided as described above, is because a sufficient mixture can flow into a cylinder by use of an inertia of intake. 0n the contrary, the exhaust valve opens before completion of a power stroke to quickly exhaust a gas.
In the intake and exhaust valves, each valve clearance is adjusted by a valve train. The valve train includes a cam shaft rotated by power of the engine, a cam shaft floor pressed by a nose of a cam according to the rotating of the cam shaft, and a lash adjuster disposed at an end of the cam shaft floor for adjusting a clearance between a stem end of the valve and the cam shaft floor.
The valve clearance is formed in order to compensate for the thermal expansion in each part of the valve. In general, the valve clearance can be adjusted by an adjusting screw.
However, the valve clearance causes a noise to occur when the engine operates, and in case the adjustment of the valve clearance goes wrong, it causes the mixture in the cylinder to leak out in a state when the intake/exhaust valve closes.
To improve the above-described problems, a hydraulic lash adjuster as a valve clearance control system has been developed and used. Examples are disclosed in U.S. Pat. Nos. 3,805,753, 4,098,240, and 4,788,947.
Each hydraulic lash adjuster is disposed at a cylinder head and has a structure which can apply a force to a predetermined direction with respect to a rocker arm. The adjuster is operated by the oil pressure transmitted through a passage formed in the cylinder head.
In those systems, two hydraulic lash adjusters are disposed respectively on the intake and exhaust valves, for example, in the case of a 4-cylinder combustion engine, eight hydraulic lash adjusters should be used.
When the adjuster is disposed on each intake and exhaust valve as described above, there are problems that a layout of the cylinder head is complicated and costs are increased by installing a large number of components.